Iron deficiency impairs skeletal muscle metabolism. The underlying mechanisms are incompletely characterised, but animal and human experiments suggest the involvement of signalling pathways co-dependent upon
oxygen and
iron availability, including the pathway associated with
hypoxia-inducible factor (HIF). We performed a prospective, case-control, clinical physiology study to explore the effects of
iron deficiency on human metabolism, using exercise as a stressor. Thirteen
iron-deficient (ID) individuals and thirteen
iron-replete (IR) control participants each underwent 31P-magnetic resonance spectroscopy of exercising calf muscle to investigate differences in oxidative phosphorylation, followed by whole-body cardiopulmonary exercise testing. Thereafter, individuals were given an intravenous (IV) infusion, randomised to either
iron or saline, and the assessments repeated ~ 1 week later. Neither baseline
iron status nor IV
iron significantly influenced high-energy
phosphate metabolism. During submaximal cardiopulmonary exercise, the rate of decline in blood
lactate concentration was diminished in the ID group (P = 0.005). Intravenous
iron corrected this abnormality. Furthermore, IV
iron increased
lactate threshold during maximal cardiopulmonary exercise by ~ 10%, regardless of baseline
iron status. These findings demonstrate abnormal whole-body energy metabolism in
iron-deficient but otherwise healthy humans.
Iron deficiency promotes a more glycolytic phenotype without having a detectable effect on mitochondrial bioenergetics.